Production of slaked lime

Abstract

A method of producing an aqueous suspension of calcium hydroxide which comprises passing a gaseous flow incorporating particles of calcium carbonate through a calcining furnace thermally to decompose the calcium carbonate, delivering a flow of the decomposition products formed in the furnace comprising calcium oxide particles suspended in gas comprising carbon dioxide to a vessel wherein the calcium oxide particles are contacted with water to produce an aqueous suspension of calcium hydroxide and separating the aqueous suspension from the said gas.

We claim: 
     
       1. A method of producing an aqueous suspension of calcium hydroxide which comprises passing a gaseous flow incorporating particles of calcium carbonate through a calcining furnace to thermally decompose the calcium carbonate and produce a gas comprising decomposition products including carbon dioxide and having calcium oxide particles suspended therein, delivering a flow of said gas comprising said decomposition products and having said calcium oxide particles suspended in said carbon dioxide as a carrier gas, without further separation of said decomposition products, to a vessel wherein the calcium oxide particles are contacted with sprayed water to produce a flow of calcium hydroxide suspended in the carrier gas, delivering the flow of calcium hydroxide to a gas/liquid separator, and separating the calcium hydroxide from the carrier gas in the separator. 
     
     
       2. A method as claimed in claim 1 and wherein said gas comprising said decomposition products and having said calcium oxide particles suspended therein is cooled before being supplied to the said vessel. 
     
     
       3. A method as claimed in claim 1 and wherein the said vessel comprises a scrubber wherein flowing water in a spray is contacted with the particles in the gaseous flow. 
     
     
       4. A method as claimed in claim 3 and wherein the scrubber includes a venturi nozzle which permits suction and swirling of the gaseous flow and intimate contacting of the calcium oxide particles in the gaseous flow by the water. 
     
     
       5. A method as claimed in claim 1 and wherein the temperature of the flow of decomposition products is reduced in the said vessel below the boiling point of water in the vessel to avoid drying of the calcium oxide particles. 
     
     
       6. A method as claimed in claim 1 and wherein the calcium hydroxide suspended in the carrier gas formed in the said vessel is passed to a second vessel wherein the mixture is further contacted with water. 
     
     
       7. A method as claimed in claim 6 and wherein the second vessel comprises a scrubber including a venturi throat. 
     
     
       8. A method as claimed in claim 6 and wherein the water added in the second vessel comprises a flow of calcium hydroxide already produced in the method and recirculated as an input to the second vessel. 
     
     
       9. A method as claimed in claim 6 and wherein the calcium hydroxide suspended in the carrier gas is passed through the second vessel in which it is further contacted with water prior to delivery to the gas/liquid separator. 
     
     
       10. A method as claimed in claim 9 and wherein the calcium hydroxide separated by the gas/liquid separator is recirculated via a recirculation loop to the said second vessel and wherein one or more properties of the calcium hydroxide in the recirculation loop is monitored and/or controlled. 
     
     
       11. A method as claimed in claim 10 and wherein the calcium hydroxide is delivered via an output line from the recirculation loop to a reactor in which it is employed to produce a precipitated calcium carbonate by reaction with carbon dioxide. 
     
     
       12. A method as claimed in claim 11 and wherein the carbon dioxide is contained in a gas extracted earlier in the method. 
     
     
       13. A method as claimed in claim 1 and wherein the temperature of the calcium hydroxide separated by the gas/liquid separator is adjusted by passing the calcium hydroxide through a heat exchanger in a recirculation loop to an output of the gas/liquid separator. 
     
     
       14. A method as claimed in claim 1 and wherein the calcining furnace comprises a flash calciner which comprises a furnace in which a toroidal flow heating zone is established to provide the flash calcining of feed material. 
     
     
       15. A method as claimed in claim 1 and which comprises a continuous or semi-continuous process for the production and slaking of calcium oxide and the direct formation of precipitated calcium carbonate from the slaked lime so produced by reaction with carbon dioxide.